#include <stdio.h>
#include <unistd.h>
#include <wait.h>
#include <stdlib.h>
#include <string.h>
#define MAX 128

void eval (char *cmdline);  
int parseline (char *buf, char **argv);
int builtin_command(char **argv);

int main()
{
    char cmdline[MAX];
    
    while(1){
        printf("root@-VirtualBox:lyx-myshell$ ");
        fgets(cmdline,MAX,stdin);
        if(feof(stdin))
        {
            printf("error");
            exit(0);
        }
        eval(cmdline);
    }
}

void eval(char *cmdline)
{
    char *argv[MAX];
    char buf[MAX];
    int bg;
    pid_t pid;
    strcpy(buf,cmdline);
    bg = parseline(buf,argv);
    if(argv[0]==NULL)
        return;
    if(!builtin_command(argv)) 
    {   
    if((pid=fork()) == 0)
    {
        if(execvp(argv[0],argv) < 0) {
            printf("%s : Command not found.\n",argv[0]);
            exit(0);
        }
    }

    if(!bg){
        int status;
        if(waitpid(-1,&status,0) < 0) 
            printf("waitfg: waitpid error!");
    }
    else
        printf("%d %s",pid, cmdline);
    return;
    }
}

int builtin_command(char  **argv)
{
    if(!strcmp(argv[0], "quit"))
        exit(0);
    if(!strcmp(argv[0],"&"))
        return 1;
    return 0;
}

int parseline(char *buf,char **argv)
{
    char *delim;
    int argc;
    int bg;

    buf[strlen(buf)-1]=' ';
    while(*buf && (*buf == ' '))
        buf++;

    argc=0;
    while( (delim = strchr(buf,' '))){  
        argv[argc++] = buf;
        *delim= '\0';
        buf = delim + 1;
        while(*buf && (*buf == ' '))
            buf++;
    }

    argv[argc] = NULL;
    if(argc == 0)
        return 1;
    if((bg=(*argv[argc-1] == '&')) != 0)
        argv[--argc] = NULL;
    return bg;
}
